I've tried a 90mm Schneider Angulon on my Speed Graphic. The short focal length means the standard sits on the bed within the camera body, this seems much less stable than the bed outside the camera body on the front door, is there something wrong with the inner bed of my Speed graphic or is there any other fix for this?

Run the rails (yoke) out fully then back in. On going back into the case section does the rear section shift in any direction? Is the rear section of the rails stable when on the bed and loose (side to side play) when in the body?

Refer to Guide Alignment and Adjustment manual page 18 Paragraph 5 of the previous post linked manual. Shift up/down loosen bed guide screws and add/remove shims as necessary to obtain a smooth even transition from the bed to the body.

Loose (side to side) movement of the rear rail section in the body-adjust the guides. If the camera was closed with the rails not fully retracted then the guides may have been broken. Sometimes the guides can be transposed to correct the play.

Guides-IPB figure 7 index 20b and 20c (page 37).
Guide shims-IPB figure 3 index 40 (page 30)._________________The best camera ever made is the one that YOU enjoy using and produces the image quality that satifies YOU.